UNIVERSITY  OF  ILLINOIS 


Agricultural  Experiment  Station 


URBANA  ILLINOIS,  MAY,  1913 


CIRCULAR  NO.  166 


A  METHOD  FOR  THE  IMPROVEMENT  OF  BUTTERMILK 

FROM  PASTEURIZED  CREAM 

By  LeRoy  Lang 

Assistant  in  Dairy  Manufactures 


At  the  present  time  there  is  a  general  demand  for  pasteurized 
dairy  products,  showing  that  the  public  appreciates  clean,  safe 
food.  The  pasteurization  of  cream  for  butter-making  is  becom¬ 
ing  more  general,  and  while  this  process  enables  the  buttermaker 
to  produce  uniform  butter  it  has  a  subsequent  detrimental  effect 
upon  the  buttermilk. 

The  buttermilk  from  pasteurized  cream  is  thin  and  watery, 
usually  lacking  in  flavor,  and  wheys  off  very  readily ;  it  may  also 
lack  the  desired  buttermilk  acidity  which  the  trade  demands. 
Because  of  these  defects,  many  creameries  are  losing  the  oppor¬ 
tunity  to  supply  the  current  demand  for  good  buttermilk.  Some 
creamery  operators  insist  that  the  loss  due  to  the  decreased  demand 
for  buttermilk  from  pasteurized  cream  is  equal  to  2  cents  per 
pound  on  the  butter.  The  economical  disposal  of  the  by-product 
of  the  creamery  is  more  important  than  the  development  of 
creamery  side  lines. 


The  method  described  in  this  circular  for  improving  butier- 
milk  from  pasteurized  cream  has  been  tried  at  the  University  of 
Illinois  Creamery  and  has  proved  to  be  very  successful.  It  con¬ 
sists  in  adding  to  the  pasteurized  buttermilk  about  10  percent  of  a 
starter  prepared  from  a  culture  sold  under  the  commercial  name 
of  Bacillus  Bulgaricus.  When  properly  made,  this  preparation 
both  furnishes  a  pleasant  acid  and  changes  the  thin  pasteurized 
buttermilk  into  a  heavy-bodied  product  with  all  the  pleasing 
characteristics  of  raw  buttermilk. 

In  ordering  the  commercial  culture  of  Bacillus  Bulgaricus, 
the  purpose  for  which  it  is  to  be  used  should  be  specified  and  the 
culture  which  makes  the  milk  viscous  should  be  requested. 

Since  this  product  is  made  from  nine  parts  of  buttermilk 
and  one  part  of  skim  milk,  it  should  not  be  sold  under  the  name 
“buttermilk”  unless  the  other  ingredients  are  also  named  on  the 
label.1  It  differs  frem  the  ordinary  commercial  Luttcimilk, 
which  is  made  by  ripening  two  equal  amounts  of  skim  milk,  one 
with  a  commercial  butter  culture  and  the  other  with  a  com¬ 
mercial  culture  of  Baciilus  Bulgaricus*  and  churning  the  two 
lots  together. 

This  preparation  of  pasteurized  buttermilk  will  be  of  interest 
to  many  creameries  where  the  manufacture  of  the  ordinary 
commercial  buttermilk  is  impossible. 

Apparatus 

The  Bacillus  Bulgaricus  culture  develops  best  at  tempera¬ 
tures  between  95°  and  100°  F.  This  is  20°  to  30c  above  the  best 
temperature  for  the  growth  of  the  ortam-ripening  cultures.  It 
has  been  found  convenient  to  hold  the  quart  bottles  or  eight- 
gallon  cans  in  which  the  cultures  are  being  developed  in  a 
wash  sink  30  x  20  x  16  inches  deep.  By  means  of  water  and 
steam  connections,  the  sink  is  kept  full  of  water  at  a  tempera¬ 
ture  between  95°  and  100°  F.,  thus  serving  the  purpose  of  an  in¬ 
cubator.  The  quart  bottles  are  supported  by  a  rack  so  that  they 
are  immersed  within  three  inches  of  the  top. 

With  this  arrangement  it  is  necessary  to  warm  the  water  by 
the  admission  of  steam  about  every  six  hours  in  order  that  the 
temperature  may  be  maintained  between  95c  and  100°  F.  Besides 
the  bottle  rack,  this  sink  holds  an  eight-gallon  can  for  the  bulk 
culture. 

The  sink  and  bottle  rack  are  also  used  for  pasteurizing  milk 
in  bottles  for  culture  propogation. 

i  Ruling  of  Board  of  Food  and  Drug  Inspection.  Bureau  of  Chemistry,  U.  S.  Dept  of  Agr. 


ILLINOIS  STATE  LIBRARY 


Preparing  Skim  Milk  for  the  Culture 

Care  must  be  exercised  in  the  selection  of  skim  milk  for  the 
propogation  of  the  first  mother  culture.  If  the  skim  milk  is  fresh 
and  clean  and  pasteurized  twice  at  a  temperature  of  185°  F.  for 
thirty  minutes,  allowing  between  pasteurizations  an  interval  of 
six  to  ten  hours,  during  which  the  milk  is  held  al  00°  F.,  a  good 
milk  fur  the  culture  is  insured.  With  ordinary  creamery  milk, 
which  often  has  an  acidity  approaching  .2  percent,  or  is  not  clean, 
it  is  advisable  to  pasteurize  the  milk  three  times  at  intervals  of  six 
hours  before  inoculating  the  first  culture. 

The  pasteurization  may  be  made  either  in  quart  bottles  or  in 
the  starter  can.  If  in  bottles,  they  should  be  thoroly  scalded  with 
boiling  water  before  the  milk  from  the  starter  can  is  placed  in 
them.  (Quart  bottles  should  be  filled  only  three-fourths  full.) 
Begin  to  count  time  of  pasteurization  when  the  milk  reaches  the 
temperature  of  185°  F.  When  pasteurizing  milk  in  quart  bottles 
set  in  a  vat  of  w7ater,  it  requires  from  tw7enty-five  to  thirty 
minutes  to  heat  the  milk  to  185°  F.  after  the  water  surrounding 
the  bottles  attains  a  temperature  of  100°  F.  A  can  of  milk  set  in 
water  at  190°  F.  requires  frcm  fifteen  to  twenty  minutes  to 
bring  the  milk  temperature  to  185°  F. 

Creamery  skim  milk  thoroly  pasteurized  and  containing 
less  than  .2  percent  acidity  furnishes  milk  of  a  satisfactory 
quality  for  all  propogations  except  the  first  one.  However,  if 
there  is  any  doubt  as  to  the  thoroness  of  the  pasteurization,  the 
milk  should  be  re-pasteurized,  or,  if  the  pasteurized  milk  is  to  be 
held  six  to  ten  hours  before  it  is  inoculated,  the  periodic  pasteuri¬ 
zations  always  insure  better  results.  Since  the  spore  forms 
vegetate  in  a  few  hours,  very  poor  milk  may  result  from  one 
pasteurization,  and  when  creamery  pasteurized  milk  is  held 
several  hours  in  the  starter  can  and  not  cooled,  a  sweet  curd  is 
a  common  result.  This  is  caused  by  organisms  w7hich  are  in  a 
dormant  condition  when  heated  but  vegetate  and  multiply  rapidly 
after  the  pasteurization  is  finished  and  the  temperature  has  not 
been  sufficiently  reduced  to  check  their  growth. 

If  the  milk  for  the  mother  culture  or  bulk  culture  cannot  be 
inoculated  at  once,  it  should  be  cooled  and  then  w7armed  to  a 
temperature  between  95°  and  100°  F.  just  before  the  inoculation 
is  made.  The  temperature  for  the  best  growth  of  Bulgaricus  is 
also  favorable  for  gas  organisms  and  the  dormant  forms  before 
mentioned,  but  if  the  Bulgaricus  is  given  opportunity,  it  w7ill 
predominate  and  produce  a  fine  heavy-bodied  culture. 


o 

Preparation  of  Mother  Cultures 

As  a  matter  of  convenience  it  is  desirable  to  develop  cultures 
in  quart  bottles,  taking  especial  care  to  keep  them  pure  and  active ; 
these  are  called  “mother  cultures.”  In  order  to  obtain  sufficient 
material  for  adding  to  the  buttermilk,  similar  cultures  are  de¬ 
veloped  in  cans  and  referred  to  as  “bulk”  cultures. 

After  the  milk  in  the  bottles  is  cooled  to  100°  F.,  it  is  inocu¬ 
lated  with  the  commercial  culture  of  Bacillus  Bulgaricus,  which 
may  be  obtained  from  any  dairy  bacteriological  laboratory. 

.  After  the  addition  of  this  culture,  the  temperature  is  maintained 
betweer.  95°  and  100°  F.  for  twenly-four  hours. 

If  the  first  propogation  of  B.  Bulgaricus  is  made  carefully, 
the  desirable  characteristics  will  be  more  evident  in  the  first  cul¬ 
ture  of  that  mother  starter  than  they  will  be  in  a  first  transfer  of 
the  ordinarv  butter  culture. 

The  Bulgaricus  Bacillus  grows  rapidly  and  produces  acid 
much  faster  and  in  larger  quantities  than  does  the  common  lactic 
acid  germ.  Several  of  the  Bulgaricus  propogalions  produce  2y2 
percent  acid  in  forty-eight  hours.  Of  150  mother  cultures 
grown  from  four  primary  cultures,,  an  average  acidity  of  1.49 
percent  was  produced  in  twenty-four  hours.  This  production  of 
acid  is  so  rapid  that  the  first  culture  acquires  1  percent  or  more 
of  acid  in  twenty-four  hours  and  the  curd  formed  is  viscous  and 
ropy. 

The  second  propogation  is  made  on  the  day  following 
the  first  inoculation.  Milk  from  the  starter  can  that  has  been 
pasteurized  to  185°  F.  for  thirty  minutes  may  be  used,  but  if 
pasteurized  twice  better  results  are  assured.  The  quart  bottle  is 
thoroly  scalded  and  the  milk  placed  in  it  as  on  the  previous  day. 
A  milk-testing  pipette  of  17.0-cc.  capacity,  dipped  in  boiling  water 
before  being  used,  serves  as  a  very  convenient  instrument  for 
inoculating  the  second  bottle  from  the  first.  The  first  mother 
culture  is  shaken  with  a  rotary  motion,  and  the  pipette  of  cul¬ 
ture  is  removed  and  placed  in  the  bottle  of  pasteurized  milk,  thus 
inoculating  the  second  culture  with  17  to  18  cc.  from  the  first 
culture  grown.  This  second  culture  is  also  shaken  with  a  rotary 
motion  and  then  placed  in  the  bottle  rack.  This  rack  may  be  kept 
permanently  in  the  sink  of  water,  or  improvised  incubator,  at  a 
temperature  between  95°  and  100°  F.  The  next  day  the  sec¬ 
ond  propogation  is  inoculated  into  the  third  mother  culture  just 


6 


as  on  the  previous  day  the  lirst  propogation  was  inoculated  into 
the  second  culture.  The  remainder  of  the  second  mother  cu  ture 
is  then  ready  for  use  in  ten  to  twenty  gallons  of  milk,  for  the 
production  of  a  bulk  culture  of  Bulgaricus. 

Preparation  of  Bulk  Culture 

In  making  the  bulk  culture,  use  a  pint  or  a  pint  and  one-half 
of  mother  culture  for  every  ten  gallons  of  pasteurized  milk. 
Mix  the  culture  thoroly  thruout  the  milk  and  hold  at  a  tempera¬ 
ture  between  95°  and  100°  F.  for  eighteen  to  twenty-four  hours, 
or  until  it  has  an  acidity  varying  from  1.2  to  1.5  percent.  The 
body  of  the  culture  should  be  viscous  and  heavy.  The  aver¬ 
age  acidity  produced  in  the  bulk  cultures  which  were  used 
for  buttermilk  improvement  was  1.58  percent  in  twenty-four 
hours. 

The  characteristic  of  the  Bulgaricus  culture  is  the  heavy, 
viscous  consistency  of  the  curd  which  is  formed.  The  viscosity 
of  the  culture  which  is  necessary  for  buttermilk  improvement  is 
obtained  when  the  proportion  of  acid  approximates  1  percent. 
The  viscosity  is  not  increased  by  holding  a  culture  and  producing 
acid  above  1.5  percent.  Furthermore,  if  the  acid  exceeds  this 
amount,  a  sharp  acid  flavor  is  likely  to  result.  However,  there 
may  be  trade  conditions  making  it  advisable  to  use  a  high  acid 
bulk  culture. 

The  cultures  do  not  always  develop  alike.  The  rapid  growing 
ones  are  most  desirable,  and  are  fully  developed  in  eighteen 
hours.  If  the  bulk  culture  is  not  to  be  used  at  once,  it  should  be 
cooled  to  50°  F.,  or  lower,  to  check  further  acid  development. 
If  possible,  it  should  be  placed  in  Ihe  refrigerator;  in  this  way  it 
may  be  kept  for  three  days  without  injury,  altho  the  acid 
gradually  increases. 

The  bulk  culture  may  be  propogaled  in  ordinary  five  or  ten- 
gallon  milk  cans.  However,  after  Ihe  culture  is  developed  it 
should  not  be  held  for  any  length  of  time  in  metal  conlainers 
but  should  be  placed  in  earthen  or  enamel  ware  in  order  to  avoid 
a  metallic  flavor  caused  by  the  action  of  the  acid  upon  the 
metal. 

Mixing  Bulgaricus  With  Pasteurized  Buttermilk 

The  amount  of  bulk  culture  which  should  be  mixed  with  the 
pasteurized  buttermilk  depends  upon  the  acidily  and  body  of  the 
buttermilk  the  trade  demands,  and  the  quality  of  the  pasteurized 


/ 


buttermilk  which  is  to  be  improved.  Ordinarily,  by  mixing  from 
ten  to  fifteen  gallons  of  bulk  culture  with  one  hundred  gallons 
of  pasteurized  buttermilk  a  very  satisfactory  product  is  obtained. 
When  the  culture  is  poured  into  the  buttermilk,  it  should  be 
mixed  thoroly  by  stirring;  it  is  not  at  all  necessary  to  churn  the 
mixture,  in  fact,  churning  will  reduce  the  viscosity.  The  acidity 
of  this  treated  buttermilk  will  range  from  .65  to  .85  percent. 

At  the  University  creamery  the  buttermilk  as  sold  is  a  mix¬ 
ture  of  one  gallon  of  culture  to  nine  gallons  of  pasteurized 
buttermilk.  The  bulk  culture  is  added  to  buttermilk  fresh  fn  m 
the  churn.  The  acidity  of  this  buttermilk  when  prepared  varies 
from  .7  to  .8  percent,  and  it  does  not  whey  off  appreciably 
in  forty-eight  hours. 

Cultures  Made  From  Skim-Milk  Powder 

Where  it  is  impossible  to  get  good  clean  skim  milk,  it  may 
be  necessary  to  use  skim-milk  powder.  In  making  the  milk,  use 
three-fourths  of  a  pound  of  skim-milk  powder  to  a  gallon  of 
pure  water.  Proceed  with  this  milk  the  same  as  with  ordinary 
skim  milk,  pasteurizing  it  at  a  temperature  between  185°  and  190° 
F.  for  thirty  minutes.  The  cultures  made  from  skim-milk 
powder  have  a  distinct  caramelized  flavor;  however,  after  the 
bulk  culture  is  ad  led  to  the  buttermilk,  this  flavor  is  scarcely 
noticeable  and  not  objectionable. 


